Studium a vývoj směsných bentonitových pojiv

Abstract

Privileged position in foundry technology of moulds and cores manufacturing has a bentonite binder that belongs to binders agent of I. generation (binding properties are determined by various physical forces). Using of moulding mixtures bonded with bentonite presents economically and technologically useful way of mould and core production and it allows making of moulds by “green sand” technology (up to 5 % of water). It is estimated that about 70 – 80 % of the world casting production from graphitizing ferrous alloys is manufactured in moulds made from this type of mixture. For the purpose of obtaining the castings with high surface quality the carriers of pyrolysis carbon (PC), especially carbonaceous matters, are added into bentonite moulding mixtures. Today the most used carrier of PC is black coal (sea coal). Some physico – chemical processes can proceed in moulds in the course of solidification. Two types of products (solid and gas) arise from the thermal exposure. A very technologically important solid pyrolysis products are formed (semicoke; Pyrolysis Carbon – PC) during combustion of PC carrier (pyrolysis). Second group of products is represented by gas compounds, which have negative influence on environment and ecological conditions of casting production (Volatile Organic Compound = VOC; sum of benzene-toluene-ethylbenzene and xylene = BTEX). In addition, a presence of carbonaceous additives in waste moulding mixtures increases a cost of depositing the waste. These mixtures belong in group of dangerous wastes. Growing emphasis on ”ecological industrial manufacture” requires a decrease of organic air pollution. There are two possible ways of solution of this situation. The first approach can represents a partial and/or total substitution of original carriers of PC (black coal) by materials with specific physico – chemical properties. Development of concentrated carriers of PC that amount will be lower in a mould is another way of solution. Keeping of surface casting quality and technological properties of bentonite mixture must be observed. The doctoral thesis summarizes a research of new materials in order to find optimal additives, which will be substitute the original carriers of PC (black coal) like composite bentonite binder or concentrated carrier of PC. The main aim of research is ensuring of surface quality of casting, decreasing of BTEX amount and keeping of physico – chemical properties of bentonite moulding mixture.